Scanner with floating backstop

ABSTRACT

A scanner having a frame assembly for supporting a movable document reading head for scanning movement in a scanning path in a first direction has a document transport to transport a document through the scanner and a drive to move the reading head across the document to read at least a portion of the document, the reading head having an optical imaging assembly including a frame supporting an imaging platen, the scanner including a floating document backstop opposite the imaging platen and extending across the scanning path to precisely position a document on the platen during an imaging operation. In a preferred embodiment the scanner includes a printing head with a comounted printing head.

CROSS REFERENCE TO RELATED APPLICATIONS

Attention is directed to copending U.S. application Ser. No. 07/451,056,filed Jul. 2, 1990, entitled Compact Multimode Input and Output Scanner;U.S. Pat. No. 5,162,916 entitled Compact Read/Write Scanner; U.S. Pat.No. 5,032,922 entitled Platen Accessory For Portable Copier and U.S.Pat. No. 5,077,614 entitled Scanner With Document and Copy SheetRegistration Means. Attention is also directed to copending U.S.application Ser. No. 07/703,083 entitled Indexing Mechanism for CompactScanner; U.S. Ser. No. 07/702,989 entitled Scanning Carriage Drive andImage Timing; U.S. Pat. No. 5,153,736 entitled Toggling Sheet TransportAnd Registration System and U.S. Pat. No. 5,153,738 entitled SingleActuator Scanner, all filed concurrently herewith and commonly assigned.

BACKGROUND OF THE INVENTION

The present invention relates to a very low cost portable compactscanner employing a single scanning carriage incorporating a readinghead and optionally a printing head to permit the reading of an originaldocument or when the scanning carriage has both a reading head and aprinting head it can provide essentially simultaneous reading andwriting of an original document and a copy. More particularly, it isdirected to a floating document backstop to precisely locate a documenton the imaging platen during an imaging operation.

Historically, copies of original documents have been produced by axerographic process wherein the original document to be copied is placedon a transparent platen, either by hand or automatically through the useof a document handler, and the original document illuminated by arelatively high intensity light. Image rays reflected from theilluminated document are focused by a suitable optical system onto apreviously charged photoconductor, the image light rays functioning todischarge the photoconductor in accordance with the image content of theoriginal to produce an electrostatic latent image of the original on thephotoconductor. The electrostatic latent image so produced is thereafterdeveloped by a suitable developer material commonly referred to astoner, and the developed image transferred to a sheet of copy paperbrought forward by a suitable feeder. The transferred image isthereafter fixed to the copy paper by fusing to provide a permanent copywhile the photoconductor is cleaned of residual developer preparatory torecharging. More recently, interest has arisen in electronic imagingwhere, in contrast to the aforedescribed xerographic system, the imageof the document original is converted to electrical signals or pixelsand these signals, which may be processed, transmitted over longdistances, and/or stored, are used to produce one or more copies. Insuch an electronic imaging system, rather than focusing the light imageonto a photoreceptor for purposes of discharging a charged surface priorto xerographic development, the optical system focuses the image raysreflected from the document original onto the image reading array whichserves to convert the image rays to electrical signals. These signalsare used to create an image by some means such as operating a laser beamto discharge a xerographic photoreceptor, or by operating some directmaking system such as an ink jet or thermal transfer printing system.

It is generally advantageous if the normally separate document readingand copy printing operations could be combined. If some of thesereading/writing functions could be combined, system operation andsynchronization could be simplified and system cost reduced through theuse of fewer parts.

In the above cross-referenced previously filed applications, an inputoutput scanner concept is described wherein a single pair of paper pathrolls drive both the document at the 12 o'clock position and the copypaper at the 6 o'clock position and the circumference of each roll isequal to the width of the reading head and the writing head. Thescanning carriage has secured thereto a reading head and a printing headwhich carriage system scans across a document scanning a band ofinformation across the document and prints a band of information acrossa copy sheet. The carriage system has a separate indexing mechanism toindex the document and copy sheet to a second position to scan anotherband of information across the document. Between imaging scans both thepaper and the document are advanced exactly the same amount by onecomplete revolution of the drive rolls thus eliminating the need fortight control of the run out tolerances on the rolls thereby insuringlower costs for the parts.

Most copiers, printers, facsimile machines and scanner devices usemultiple electromechanical actuators such as motors, clutches,solenoids, etc. to operate the various components of the machine atvarious times in the processing cycle. Even in the compact combinedinput/output scanner described in the above cross-referenced previouslyfiled applications, there were two motors required. One was used to movethe scanning carriage and the second was used to advance both thedocument and the copy paper. For each electromechanical actuator, thereare costs which must be born besides the unit cost of the actuatoritself. These include a power supply to drive the device, harness coststo carry the power and control signals to the device, assembly costs toinstall the device, the power supply and the harness and electroniccircuitry to control the devices and often some kind of voltage controlcircuitry to ensure proper operation of the devices over a wide range ofoperating voltages.

In addition, in the above-referenced previously filed application thecircumference of the index drive roll is equal to 384 pixels at 16 permillimeter which means its diameter is about 7.7 millimeters which meansthat the optical system must fit within the 7.7 millimeters heightconstraint. The present invention is directed to meeting thisarchitectural constraint with the minimum number of parts at the lowestcost.

PRIOR ART

U.S. Pat. No. 4,920,421 to Stemmle discloses an architecture includingcombing an input and output scanner and a fixed platen with a carriagesystem for scanning across the document and reading a band ofinformation and printing it on a copy sheet, then indexing the carriageto the next band of information on the document while advancing the copypaper the same distance relative to the copy sheet support on thecarriage.

In addition, there are several hand held scanners which are batteryoperated and produce only a copy of a relatively small or partial bandof information, rather than a full copy of an 81/2×11 sheet. Forexample, the Casio™ copy pen is an example of such a handheld batterypowered scanner which uses manual operation to scan an 8 millimeterportion of a document which is stored and printed on plain paper bymanually moving the printhead on the other end across the paper. Othersimilar devices read a document and simultaneously write a copy onthermal paper as it is unrolled from a paper supply on board the handheld copier. None of these devices have document or paper transport.

SUMMARY OF THE INVENTION

The present invention is directed to an input scanning system of ultrasimplicity, very low cost and a high degree of portability.

In accordance with the principle aspect of the present invention ascanner having a movable document reading head for scanning movement ina scanning path in a first direction across a frame assembly has meansto transport a document through the scanner and a reading headcomprising an optical imaging assembly including a frame supporting animaging platen, the scanner including a floating document backstopopposite the imaging platen and extending across the scanning path toprecisely position a document on said platen during imaging operations.

In a further aspect of the present invention the imaging assemblyincludes an image illuminator, a lens and an input sensor having anarray of photosites.

In a further aspect of the present invention the floating documentbackstop is rigid with a reflective white surface.

In the further aspect of the present invention the scanner has top coverfor the frame assembly and movably supports the floating documentbackstop.

In a further aspect of the present invention the scanner includes amovable printing head and means to transport a copy sheet through thescanner in a copy sheet transport path and means to move said printinghead across said copy sheet to print at least a portion of said documentcorresponding to that portion read by said reading head.

In a further aspect of the present invention the scanning carriageincludes solid state devices with reading and printing elementsrespectively, securely comounted to a mounting substrate.

In a further aspect of the present invention the reading head produces adigital image and is electrically connected to the printing head forprinting a digital image on a copy sheet.

In a further aspect of the present invention the means to transport adocument and copy sheet include means to index a document through adocument path in a direction transverse to the scanning direction and toindex a copy sheet through a copy sheet path in the opposite transversedirection of indexing said document.

In a further aspect of the present invention the reading and printingoccur essentially simultaneously without image storage.

In a further aspect of the present invention the right side pixel of theread head coincides with the lead edge of a portion of a document to becopied and the left side pixel of the printhead coincides with the leadedge of the print of said portion on a copy sheet to form a rightreading image on the copy sheet.

In a further aspect of the present invention the scanning carriage ismovably mounted between the plane of the document transport path and theplane of the copy sheet transport path.

In a further aspect of the present invention the indexing meanssimultaneously indexes a document in the document transport path and acopy sheet in the copy sheet transport path.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is had tothe accompanying drawings wherein the reference numerals have beenapplied to the same parts in several figures.

FIGS. 1A, 1B, and 1C are three isometric views illustrating the generaloperation of the compact copier.

FIG. 2 is an isometric view of the compact scanner according to thepresent invention with the top cover removed.

FIG. 3 is a schematic cross sectional view of the compact scanneraccording to the present invention.

FIG. 4 is an enlarged sectional view illustrating the elements of thescanning carriage in the present invention

FIG. 5 is an illustration of the scanning operation.

FIGS. 6A, 6B and 6C illustrate the cam operation of the single actuatorcopier concept.

FIGS. 7A and 7B show the cam unwrapped to a flat profile.

FIG. 8 is a isometric view of the copy sheet registration gate and idlerroll arrangement.

FIG. 9 is a sectional view of showing the floating document backstopsupported in the top cover and the scanning path of the scanningcarriage.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIGS. 1A, 1B and 1C a general overview of the compactscanner according to the present invention is provided. The scanner isgenerally illustrated as comprising a frame assembly 15 which may havemaintenance station 12 at one end and a top cover 11 pivotally mountedto the frame assembly. To make a copy of document 14 the top cover isrotated to the open position as shown in FIG. 1A, copy sheet 13 isinserted at the entrance of the copy sheet transport path and thedocument 14 is inserted against a registration stop member in the topcover after which the top cover is closed and the copying sequencebegins by the scanning carriage scanning a band of information acrossthe document. During the scanning operation the document and copy paperare both held in a fixed position and the document and copy paper areboth held in a fixed position and the image on the document is digitizedby an input digitizing system and in the preferred embodiment a digitalimage is essentially simultaneously printed by a printing system on thecopy sheet. Subsequently, the document is indexed to the right and thecopy sheet is indexed to the left to enable the scanning carriage toscan a second band of information across the document. The distance ofthe indexing of both the document and copy sheet is the width of theband of information across the document.

Referring to FIGS. 2, 3, 4, 6A, 6B and 6C of the drawings there is showna combined input scanner and output scanner designated generally byreference numeral 10. The scanner 10 includes a frame assembly 15composed of a base unit 18, rails 19 within which scanning carriage 20is transported during its scanning path. When not in scanning operationthe scanning carriage 20 is parked at the home position. If the printinghead is an ink jet head it is parked in the maintenance station 12 (seeFIG. 1A) which may perform one or more of the following functions;sealing off the head to keep it from drying out or being contaminated,clean the head, humidify the head and act as a waste sump to enable thehead to be primed.

The scanning carriage 20 includes a reading head 17 and a printing head25 mounted on substrate 52. The reading head comprises a contact imagesensor, CIS 56, including an array of light emitting diodes 21 mountedto frame 57 for illuminating a document 14 adjacent a glass platen 54,an image of which is reflected through a lens 23 such as a Selfoc lens,to an input sensor chip 26 having an array of photosites for activationby the reflected radiation which is converted to electrical signals orpixels which are processed by an application specific integrated circuit(ASIC) 27 and subsequently transmitted to the printing head 25. Theprinting head may be an ink jet chip or a thermal print head (TPH) 25printing on sensitized paper or by heating ink impregnated in a ribbon58 as illustrated in FIG. 4 or some other direct marking device.Typically, the thermal print head comprises an array of heater elements,resistors 53, which are actuated, heated, to form pixels by directcontact with thermal paper 13 or by melting a small portion of ink onribbon 58 and pressing it into plain paper 13, essentiallysimultaneously in response to the image read by the reading head. Duringthe operation the scanning carriage scans a document which is in animage plane and prints on the copy sheet which is in the printing plane.

It will be understood that while reference has been made to readingheads and printing heads that the present invention encompasses in ageneric sense solid state devices with input reading elements and solidstate devices with output printing elements. It will also be understoodthat the number of scanning elements or sensors that comprise the imagereading head 17 determine the initial scanning resolution while thenumber of heating elements 53 that comprise the printing head 25determine the resolution of the image copy. In a preferred embodimentthe number of input scanning elements equals the number of outputprinting elements. In a particularly preferred embodiment the sensorchip has 384 photosites at 400 per inch or 16 per millimeter and thethermal print head also has 384 heater elements at 400 per inch or 16per millimeter. Both the reading head and the printing head are securedfor movement on scanning carriage 20 which may be mounted forunidirectional scanning movement or forward and backward bi-directionalscanning movement in a scanning path along the length of the frameassembly by means of scan stepper motor 32 through lead screw 31 to movethe scanning carriage on the rails 19.

The movement of the scan carriage 20 supporting image reading head orassembly 21, 23, 26 and printing head 25 is further illustrated withreference to FIG. 5. Arrows 33a and 33b illustrate a forward and areverse scan of the carriage 20 across a document and copy sheet. Thearrows 68 illustrate that a number of pixels, perpendicular to thedirection of movement of scan carriage 22, are both read by the readinghead and printed by the printing head as the carriage scans the documentand copy sheet. In a typical embodiment, 384 pixels at 400 per inch areread and printed perpendicular to the movement of the carriage as itscans. In this example, arrow 68 represents a band of information 0.0025inch long and 0.96 wide which is read and printed. This enables scanninga band of information about 0.96 inches wide. The movement of thecarriage can be continuous or in discrete steps, but in a preferredembodiment, the 384 pixels are read and printed in increments that areone pixel apart as shown. In one embodiment, each time the scan carriagemoves a distance of one pixel width across the sheet, the electronicimage of 384 pixels down the sheet are moved into a shift register andthen amplified and shifted in reverse order into the print head to heatthe 384 heater elements 53 and thereby create a print of the 384 pixelspreviously read. This sequence is repeated each time the scan carriagehas moved a distance of one pixel width. It should be noted that thescanning could also be done with 384 parallel channels, each channelreading and writing a single line of pixels as the carriage sweepsacross the page. While it is preferred that the read/write operation besubstantially simultaneous it should also be noted a digital buffer orregister could be incorporated to initially store the scanned or readsignals for later printing after a predetermined or arbitrary timeperiod. It should also be understood that the combined scannerillustrated has multi-mode capability and could be operatedindependently as a printer modulated by any suitable device providingdigital information, operated independently as a scanner to convertsource documents to a digital representation, or operated as a facsimiledevice using the reading and printing elements when combined with asuitable modem, or as a copier by combining the scanning and printingoperations. As a printer only the reading head need not be included andas a scanner only the printing head need not be included.

With further reference to FIG. 2, and additional reference to FIGS. 3-8the single actuator copier will be described in further detail. The scancarriage 20 is driven by a lead screw 31 which may be attached directlyto a stepper motor 32 as illustrated in FIG. 2 or alternatively driventhrough a gear train. As the motor rotates the lead screw, the grooves40 in the lead screw engage threads (not shown) on the interior of thescan carriage to translate the read/write carriage along the lead screw.The pitch on the lead screw is selected, such that, each pulse or everysecond, third or fourth pulse, of the stepper motor corresponds to onepixel width or 1/400th inch of carriage motion. This enables the sameclock pulse generator used to drive the stepper motor to be used totrigger the read/write systems on the scanning carriage. Alternatively,a D.C. motor may be used to actuate the lead screw and together with anencoder wheel generate a signal which is used to trigger the read and/orwrite functions.

Following a scanning run in either direction across the length of theframe assembly the document and copy sheet are each indexed through thescanner in opposite directions a distance equal to the width of the bandof information on the document scanned by the reading head which is thesame as the width of the band of information printed on the copy sheetby the printing head. This width can be any width from a minimum of asingle pixel line to a maximum of the width of the entire document. Inpractical terms, however, in order to keep the cost of the read andwrite components low the width of the band is of the order of a fractionof an inch to several inches wide. The method for achieving this isillustrated with further reference to FIG. 2 and FIG. 3 wherein anindexing means is provided comprising rotatable drive rolls 35a, b, cand d mounted on drive roll shafts 36a and 36b forming feeding nips fora document with document feed idler rolls 42 contained within the topcover 11 of the scanner. The term synchronously driven is intended todefine only that the shafts 36 are synchronized to each other. The driverolls 35a, b, c and d also form feeding nips for a copy sheet with thecopy sheet idler rolls 46 in the copy sheet transport path.

With the read/write carriage in the home position, the stepper motor 32rotates the lead screw 31, which translates the carriage 20 in animaging sweep across the copier frame 15. At the completion of theimaging sweep a tab 63 on the carriage contacts a stop 64 on camactuator arm 65 which is pivotally mounted about fixed pivot 69 andmoves it in the scanning direction whereby cam drive pin 38 turns thebarrel cam 39 which is fixedly mounted to shaft 36. Attached to camactuator arm 65 at its fixed end is a spring, which may, for example, bean integrally molded plastic leaf spring 71 which is in biasedengagement at its other end with a fixed stop member 74 and is alwaysurging the cam drive pin 38 to detent into the end of a slot on thebarrel cam 39 in the home position.

In operation as the carriage moves in a first direction tab 63 engagesstop 64 causing arm 65 to rotate about pivot 69. During this motion pin38 engages a cam profiles 90 (See FIG. 7A) of barrel cams 39 on the endof the drive roll shafts 36a and b and rotates the barrel cams andshafts 36a and 36b a portion of a complete rotation. During this motionenergy is stored in leaf spring 71 as the carriage motion causes arm 65to rotate which causes spring 71 to flex. The direction of rotation ofthe motor is reversed and the translating read/write carriage is drivenin a second direction. The energy stored in spring 71 causes the arm 65to rotate in the opposite direction following the movement of thecarriage. During this motion which causes the pin 38 to engage a secondcam profile 91 on the barrel cam thus, causing a second portion ofrotation in the same direction as the first rotation. This may be morecompletely understood with reference to FIGS. 6A, 6B, 6C and 6D, whichillustrate the position of the scanning carriage at several positions,and FIGS. 7A and 7B which illustrate the cam unwrapped to a flatprofile. Thus, when the carriage moves in the first direction forforward indexing, the cam drive pin 38 advances from point A to point B,during which the cam does not rotate. As, the motion of the scanningcarriage causes the pin 38 to continue from point B to point C the camprofile 90 is engaged and the cam rotates a distance M. When motion ofthe scanning carriage is reversed the pin moves from point C to point E(see FIG. 7A) and the cam does not rotate during this motion. As thescanning carriage continues in the opposite direction enabling pin 38 tomove from point E to point A once again, the return cam profile 91 isengaged by pin 38 and the cam rotates a distance N. At point A, the camhas rotated one complete revolution, the cam actuator arm is springloaded by the preload energy stored in spring 71 to detent the pin at Ato insure that the drive roll will hold position during the subsequentscanning cycle and resist shaft 36 rotation due to perturbing forceswhich could cause pixel placement errors. When the carriage reaches aposition which corresponds to the cam pin at A the second time, thecarriage normally continues to translate in the reverse direction acrossthe imaging area until it reaches the other side of the document andcopy paper. For bi-directional reading and writing imaging would beaccomplished during this return sweep. For uni-directional reading andwriting imaging is done only in the forward direction. Unidirectionalimaging limits the pixel placement errors due to any backlash in thesystem. For 11 inch long paper 12 imaging sweeps are required for aprinthead 384 pixels wide. After the last imaging sweep of theread/write carriage, the next copying cycle can begin immediately byloading the next document and copy paper into the system.

The scanner, according to the present invention, has application withthe platen accessory described in U.S. application Ser. No. 07/547,275as described above and for purposes of returning the scanner to the homeposition automatically can be provided with a third and fourth camprofile molded into the barrel cam as illustrated in FIG. 7B.Accordingly, after the last imaging sweep the scanner will be located atthe other end of the platen from its start position. Rather thanstopping the pin 38 at position C and reversing to position A as wasdone for forward indexing, the translating carriage continues to movethe pin in the first direction past position C until it reaches positionD. At that time, the carriage alternately reverses direction to move thepin 38 between positions D and B for a total of 12 cycles. This motioncauses the pin to engage two additional cam profiles 92, 93 on thebarrel cam which rotate the drive shaft in the opposite direction tothat of the forward index and which automatically moves the copier backto its home position. After the last half cycle from position D to B,the carriage and pin continue in a second direction and thus, moving thepin to its detent position at A. Having moved the copier back to itshome position, the read/write carriage continues in a second directionacross the imaging area to the carriage home position.

With additional reference to FIG. 3, the top cover 11 is pivotallymounted to the frame assembly 15 and in particular the base unit 18 andpivots about points 41. When the top cover is pivoted to the openposition the document feed idler roll 42 are disengaged from the driverolls a registration edge is inserted into the plane of the documenttransport path enabling the placement of a document to be copied in thescanner with its lead edge registered and inhibiting transport of thedocument through the document transport path. In a preferred embodimentthe circumference of the drive rolls is equal to the width of the bandof information across the document scanned by the scanning carriage toeliminate run out and shaft straightness tolerance defects whichotherwise might cause some misregistration between scan widths.

As illustrated in FIG. 3 the second pair of indexing rolls is located onthe opposite side of the lead screw from the first pair of indexingrolls. This second indexing roll pair is the same as the first, namelythey are mounted on a shaft which has a barrel cam on one end which isactuated in the same manner as the first indexing roll pair by anactuator to provide synchronization between the first and second pair ofindex rolls. With the second pair of indexing rolls deletions on the topand bottom of an image read and/or an image printed are eliminated. Withonly a single indexing roll system both the document and copy sheet mustbe loaded into the single nip which means that the distance from the nipto the image area is a deletion.

Attention is directed to FIG. 8 illustrating the copy sheetregistration, mechanism wherein the read/write carriage 20 engages aramp 48 on a toggling link 49 just before it reaches its home position.This engagement and further motion of the read/write carriage causes thetoggling link 49 to rotate about a pivot 50 and the other end of thetoggling link 49 lifts the registration gates 60 into the paper path asshown in the FIG. 8. The registration gates 60 are mounted on a pivotingframe 61, which has the copy paper idler rolls 46 mounted on theopposite side of the pivot 51 for this frame. Accordingly, when theregistration gates 60 are lifted the copy paper idler rolls 46 aresimultaneously disengaged from the drive rolls. This motion opens thenips and allows the operator to insert a piece of copy paper for thenext copying job. When the read/write carriage moves in a firstdirection away from the home position, this motion also allows togglelink 49 to return to its initial position which drops the registrationgates out of the paper path and engages the idler rolls to the driverolls, thus, capturing and holding the copy paper in position during theimaging sweep, and providing a drive force on the copy paper during theindex cycle at the end of the imaging sweep.

When the top cover is opened the idler rolls in the document path whichare mounted in the top cover are moved out of position enablingplacement of the document against the front registration edge which ispart of the top cover assembly. Following insertion of the copy sheetthe top cover is closed thereby re-engaging the document idler rollswith the drive roll. In addition, two sensors (not illustrated) detectthat both the document and the copy paper have been loaded, andaccordingly, the logic initiates the copying sequence. The scan carriagecontaining the reading and writing heads moves from the home position,dropping the registration gates out of the paper path and engaging thecopy paper idler rolls to the drive rolls, scans across the document andcopy sheet while both remain stationary. The document is positioned sothat its lead edge coincides with the right side pixel of the read head,and the copy paper is positioned so that its lead edge coincides withthe left side pixel of the print head. This enables the formation of aright reading image on the copy sheet. A line of information on thedocument read on the right extreme of the image read head fires theprint head on the extreme left of the printing array during the scan ofthe carriage 20. This may be illustrated with reference to FIG. 3. Thepixel data received by the input chip at the extreme right of the chip(R); as the carriage 20 moves in the direction into and out of the paperis transmitted and amplified to modulate the print head to fire theprint head at the extreme left (L) of the print head. This schemeenables the printing of right reading copies with essentiallysimultaneous reading and writing without information storage. As thecarriage scans across both the document and the copy paper, the 0.96inches band of information being read off the document is immediatelyprinted onto the copy paper. When the first imaging scan is complete thecarriage motion continues in the same direction engaging the stops 64 onthe cam actuator arm 65 causing the arm to move which rotates cam 39 andshafts 36a and b causing both both the document and copy paper to beindexed in a direction transverse to the scanning direction the width ofthe band of information previously scanned. This indexing isaccomplished by driving the drive rolls which engage the document at the12:00 position with the document feed idler rolls forming a feeding niptherebetween, and the copy paper at the 6:00 position with the copysheet feed idler roll forming a feeding nip therebetween. The clockwisemotion of the drive rolls of one revolution causes a document to beindexed 0.96 inches to the right and the copy paper to be indexed 0.96inches to the left. In this way the second band of information from thedocument is moved into a position over a scan carriage and a secondportion of the copy paper is moved to a position under the print head.The scan carriage reverses and returns to a position near the homeposition then reverses direction again to scan across the document andcopy paper in the reverse direction from the first scan again readingthe document and immediately printing the copy. This sequence isrepeated until the entire document is read and the entire copy isprinted after which time the print head returns to the home position andis parked.

With continued reference to FIG. 3 and additional reference to FIG. 9the floating document backstop 76 will be described in greater detail.The floating document backstop 76 is mounted to the top cover 11 bymeans of fixed location pins 77, one or more on each end of the covermount, the pins protruding within the slot 78 on each end of thefloating backstop enabling the backstop to be vertically, movably,engaged or floating relative to the top cover 11 and reading head 17.The floating backstop extends across the scanning path and is slightlylonger than the length of the entire sweep and slightly greater than thewidth of the scanned image. To operate the scanner, the operator pivotsthe top cover to the open position and inserts a document to registerits lead edge. When the cover is closed the document is constrainedbetween the floating document backstop and the rest of the opticalimaging assembly. When the read/write carriage scans across the documentthe floating backstop presses the document to the platen in the opticalframe on the read/write carriage only at the portion being imaged toconstrain the document into the plane of best focus. After the imagingsweep is completed the read/write carriage moves out of direct contactwith the document which then can be indexed without experiencing thedrag load created by the floating backstop trapping the document againstthe platen. While the backstop "floats" in the slots in the top cover itis preferably rigid to inhibit damaging the document by wrinkling orcreasing and has a white reflective surface to function like a regularplaten cover reflecting light from the illuminator. The floatingbackstop enables the lens in the contact image sensor to be designedwith a relatively narrow depth of focus.

Accordingly, by the present invention, an optical assembly with theminimum components all mounted onto a carriage fixed frame has beenprovided which does not require final adjustments. The rigid floatingbackstop constrains the document into the plane of best focus withoutexerting undue drag on the drive system and reduces concern for mountingtolerances.

All the patents and other references together with the cross-referencedcopending applications are hereby and specifically totally incorporatedin their entirety into this specification.

While the invention has been described with reference to specificembodiments thereof it will be apparent to those skilled in the art thatmany alternatives, modifications and variations may be made. For examplewhile the invention has been illustrated with respect to having anindexing mechanism for the document and copy sheets on only one side ofthe scanner it will be appreciated that a similar indexing mechanism maybe provided on the opposite side of the scanner. Accordingly, it isintended to embrace all such alternatives and modifications as may fallin the spirit of the appended claims.

I claim:
 1. A scanner comprising a frame assembly for supporting amovable document reading head for scanning movement in a scanning pathin a first direction, means to transport a document through saidscanner, means to move said reading head across said document to read atleast a portion of said document, said reading head comprising anoptical imaging assembly including a frame supporting an imaging platen,said scanner including a vertically movable floating document backstopopposite and on top of said imaging platen and extending across saidscanning path to precisely locate and constrain a portion of a documentbeing imaged into a plane of best focus on said platen during an imagingoperation.
 2. The scanner of claim 1 wherein said imaging assemblyincludes an image illuminator, a lens and an input sensor having atleast one photosite.
 3. The scanner of claim 1 wherein said floatingdocument backstop is rigid.
 4. The scanner of claim 3 wherein saidfloating document backstop has a reflective white surface.
 5. Thescanner of claim 1 including a top cover for said frame assembly, saidfloating document backstop being movably supported in said cover.
 6. Thescanner of claim 5 wherein said floating document backstop has mountingslots at each end which are in engagement with and vertically movablysupported by mounting pins in said top cover.
 7. The scanner of claim 1further including a movable printing head, means to transport a copysheet through the scanner in a copy sheet transport path means to movesaid printing head across said copy sheet to print an image on at leasta portion of said copy sheet.
 8. The scanner of claim 1 wherein thereading head and writing head are comounted on the same carriage.
 9. Thescanner of claim 7 wherein the reading head produces a digital image ofat least a portion of a document and is electrically connected to saidprinting head for printing a digital image corresponding to that portionof a document read by said reading head on said copy sheet.
 10. Thescanner of claim 7 wherein said reading and printing occur essentiallysimultaneously without information storage.
 11. The scanner of claim 7wherein a right side pixel of the read head coincides with a lead edgeof a portion of a document to be copied and a left side pixel of theprint head coincides with a lead edge of the print of said portion on acopy sheet to form a right reading image on the copy sheet.
 12. Thescanner of claim 7 wherein said scanning carriage is movably mountedbetween a plane of said document transport path and a plane of said copysheet transport path.
 13. The scanner of claim 7 wherein said means totransport a document and copy sheet include means to index a documentthrough a document path in a direction transverse to said firstdirection and to index a copy sheet through a copy sheet path in anopposite transverse direction of indexing said document.
 14. The scannerof claim 13 wherein said document transport path is above said copysheet transport path and said reading head and printing head areco-mounted on said scanning carriage for essentially simultaneouslyreading a document face side down in said document transport path andprinting a digital image face side up on a copy sheet.
 15. The scannerof claim 7 wherein said indexing means simultaneously indexes a documentin said document transport path and a copy sheet in said copy sheettransport path.
 16. The scanner of claim 15 wherein when said carriagemoves in said first direction the reading head scans a band ofinformation across the document and the printing head essentiallysimultaneously prints the same band of information across a copy sheetand upon completion of said scanning movement said indexing meansindexes the document and copy sheet through their respective paths adistance equal to a width of said band of information before saidcarriage scans another band of information across the document.
 17. Thescanner of claim 16 wherein drive rolls have a circumference equal tothe width of the band of information.